Survivability of Alcaligenaceae and Chromatiaceae as palm oil mill effluent pollution bioindicators under fluctuations of temperature, pH and total suspended solid

Alcaligenaceae and Chromatiaceae were previously reported as the specific pollution bioindicators in the receiving river water contaminated by palm oil mill effluent (POME) final discharge. Considering the inevitable sensitivity of bacteria under environmental stresses, it is crucial to assess the survivability of both bacteria in the fluctuated environmental factors, proving their credibility as POME pollution bioindicators in the environment. In this study, the survivability of Alcaligenaceae and Chromatiaceae from facultative pond, algae (aerobic) pond and final discharge were evaluated under varying sets of temperature (25-40°C), pH (pH 7-9) and low/high total suspended solid (TSS) contents of POME collected during low/high crop seasons of oil palm, respectively. Following treatment, the viability status and compositions of the bacterial community were assessed using flow cytometry-based assay and high-throughput Illumina MiSeq, respectively, in correlation with the changes of physicochemical properties. The changes in temperature, pH and TSS indeed changed the physicochemical properties of POME. The functionality of bacterial cells was also shifted where the viable cells and high nucleic acid contents reduced at elevated levels of temperature and pH but increased at high TSS content. Interestingly, the Alcaligenaceae and Chromatiaceae continuously detected in the samples which accounted for more than 0.5% of relative abundance, with a positive correlation with biological oxygen demand (BOD5) concentration. Therefore, either Alcaligenaceae or Chromatiaceae or both could be regarded as the reliable and specific bacterial indicators to indicate the pollution in river water due to POME final discharge despite the fluctuations in temperature, pH and TSS.